1. Field of the Invention
The present invention relates to a structure of fingerprint identification device and, more particularly, to a mobile device with high-accuracy fingerprint identification.
2. Description of Related Art
Biological feature sensing and comparing technologies have been maturely and widely applied in identifying and verifying the identity of a person. Typical biometric identification types include fingerprint, voiceprint, iris, retina identifications, and the like.
For consideration of safe, comfortable, and efficient identification, the fingerprint identification has become the most popular one. The fingerprint identification generally requires a scanning to input a fingerprint or a finger image of a user and store the unique features of the finger image and/or the fingerprint for being further compared with the fingerprint reference data built in a database so as to identify or verify the identity of a person.
The image input types of the fingerprint identification include optical scanning, thermal image sensing, capacitive sensing, and the like. The optical scanning type is difficult to be applied in a mobile electronic device due to its large volume, and the thermal image sensing type is not popular due to its poor accuracy and reliability. Thus, the capacitive sensing type gradually becomes the most important biometric identification technology for the mobile electronic devices.
FIG. 1 is a local cross-sectional view of a typical fingerprint sensing region, which illustrates a capacitive fingerprint identification sensor interacting with a fingerprint. As shown in FIG. 1, the fingerprint 130 has the ridges 140 located on sensing elements 110. Namely, the capacitive finger identification sensor has a plurality of sensing elements 110, and the fingerprint 130 presses on a non-conductive protection layer 120. In the prior art, the protection layer 120 has a thickness of about 50 μm to 100 μm, such that the sensing elements 110 can sense signals of the ridges 140 of the fingerprint 130.
However, when the protection layer 120 is made of glass and has a thickness of about 50 μm to 100 μm, it may be broken due to an inappropriate press force of the finger. FIG. 2 is another local cross-sectional view of the typical fingerprint sensing region, in which the thickness of the protection layer 120 is increased to be 200 μm to 300 μm. In FIG. 2, dimensional relationships among individual elements are illustrated only for ease of understanding, but not to limit the actual scale. When the thickness of the protection layer 120 is getting increased, the distance d1 between the ridge 140 and the sensing element 110-1 is getting close to the distance d2 between the ridge 140 and the sensing element 110-2, i.e., d1≈d2, and thus the signals sensed by the sensing elements 110-1 and 110-2 are alike, resulting in that the fingerprint cannot be sensed accurately. Thus, the prior art encounters a tradeoff problem; i.e., the layer 120 may be easily broken when the thickness is decreased, and the fingerprint sensing cannot be performed accurately if thickness of the layer 120 is increased.
Accordingly, a direct approach to solve the problem is to adopt a sapphire as a material of the protection layer 120, so as to prevent the protection layer 120 from being broken due to an inappropriate force applied thereon. However, such a way relatively increases the cost.
Therefore, it is desirable to provide an improved mobile device with fingerprint identification to mitigate and/or obviate the aforementioned problems.